The present invention relates to an image display device, more specifically, to an image display device utilizing a liquid crystal display device capable of adjusting luminance of a backlight thereof in response to brightness of environment light (surrounding light), thus rendering a displayed image discernible.
In the field of medical services, various types of diagnostic image-acquiring apparatuses utilizing X-rays and the like have been conventionally put into practical use, for example, an X-ray photographic apparatus, a computed radiographic (CR) apparatus, a computed tomographic (CT) apparatus, a magnetic resonance imaging (MRI) apparatus and the like.
Medical image information acquired with these apparatuses is used in medical sites for the purpose of diagnosis and the like, by means of the information being recorded on photographic films and observed on a film viewer (schaukasten), or being recorded on other recording media and observed on an image display device (a monitor screen) after desired imaging processing such as frequency processing, gradation processing or the like are rendered.
A cathode ray tube (CRT) display device has been conventionally used as the above-described image display device. However, recently, a so-called flat panel display that uses a liquid crystal panel, an organic electro-luminescent (EL) panels or the like is in the process of utilization. This flat panel display generally possesses advantages such as space-saving, light weight, low electric power consumption and the like. Therefore, it is conceivable that the flat panel display will become more widespread in the future.
It should be noted here that a CR (computed radiography) apparatus is a radiographic image recording and reading apparatus using an accumulative fluorescent material (stimulable phosphor) that operate as follows. First, radiation is emitted and a part of radiation energy is accumulated in the accumulative fluorescent material or the stimulable phosphor. Then, excitation light such as visible rays or infrared light is emitted onto the accumulative fluorescent material or the stimulable phosphor, whereby the stimulated luminescence is exhibited according to the radiation energy accumulated therein. In the CR apparatus, first, radiographic image information of a subject, such as a human body, is recorded on the stimulable phosphor by an X-Ray apparatus and the like. Then, the radiographic image information represented by the stimulated luminescence is photoelectrically read to obtain image signals. Then, the thus obtained image signals are subjected to image processing. Finally, the thus processed image signals are output to display a soft copy image on an image display apparatus or to record a hardcopy image on a X-Ray photographic film.
Also, a CT (computed tomography) apparatus is based on a computed tomography method, with which projection images are obtained using parallel X-ray beams on straight lines from various angles and X-ray absorption coefficients of tissues in a human body, which represents the composition of the tissues, are obtained through computation of these data. The thus obtained composition of the tissues is output as a soft copy image or a hardcopy image. The tissue composition is reconstructed from the projection images using, for instance, a successive approximation method or an inverse-projection method,
Further, a usual MRI (magnetic resonance imaging) apparatus obtains an electromagnetic wave signal generated by a nuclear magnetic resonance effect of hydrogen atoms and converts the signal into an image. In more detail, an electromagnetic wave at a natural resonance frequency of nuclei is applied from the outside to place a nuclear magnetic moment due to spins in an excitation state. Then, the application of the electromagnetic wave is terminated under this condition to have the nuclei sequentially undergo a transition from the excitation state to a ground state. During this transition, an electromagnetic wave at a resonance frequency is emitted. This electromagnetic wave is received by coils and is converted into an image. The thus converted image is output as a softcopy image or a hardcopy image.
Incidentally, the display device using the above-described liquid crystal panel has a problem that visibility of the displayed images are changed by the outside light or the environment light of the surrounding area, due to the fact that certain light leaks out even if a backlight of the liquid crystal panel is completely turned off (so-called “light leak”).
This is the problem that can be regardless when seeing in a bright place, but that it becomes considerably indiscernible when seeing in a dark place to some degree. Specifically, in slightly dark observation circumstances, the light of the liquid crystal panel seems leaking out, thus the contrast of the images thereon are deteriorated.